Imaging with Astrometrica

by Clyde Kobashigawa

prepared for TOPS 2003, KBO Recovery Project (pgs 23-37)

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5) Data reduction and Astrometry to analyze the data in the format of fits files/images received from the telescope.

I used the software called Astrometrica. You can go to the web home site http://www.astrometrica.at/ to get more information about it. Attached is just a small part of the software that I used. a) Locate the listing of what each of the image file represents, usually as

a notepad file such as n1, n2, or n3. (You may have to open the folder that you have your data and be sure to select Files of type—All Files. See Below.) See Example: Notepad #1, #2, and #3) Notice that there are columns of data without headings.

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Example: Notepad #1, #2, and #3

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b) You may want to copy and paste the data from all three notepads onto one spreadsheet, label the columns, then sort the data by the object, so that you can easily determine which of the image files are to be blinked together. (See Example: Excel Notepad) You may want to have a print out of this list to make it easier to load the respective fits file when using Astometrica.

Example: Excel Notepad

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c) Open the Astrometrica software (If you have any data that was not sent to the MPC, answer NO, to the window asking if you want to replace existing files or it will eliminate all the data. This will allow you to continue to add to your report to be submitted later.) select File, Load Images-a window will appear and you need to select and open the location and the folder that contains your fits files in the Look in: such as below.

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d) Select the first image by left clicking on the file which will be highlighted, cursor to the next file and while holding the ctrl. button down, left click, which will now have both files highlighted. Cursor to the next file you want to open and while holding the ctrl. button down, left click again. You should now have all three image files highlighted, (See below) now press Open.

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e) You should get a series of three windows that look similar to the one below. Check to see if it is the file you want to open by checking the date and the time before clicking OK.

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f) Do Data Reduction by opening Astrometry and selecting Data Reduction. A window appears as below. Click on the box with the three dots.

g) Another window appears as below, in the box labeled Filters, type in the object name then click on the magnifying glass. (See arrow)

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h) Another window appears as below, with another name for the object, you may want to note it down, then click OK. for the software to select the object. You should get another window.

i) Another window appears as below, with the coordinates RA and Dec for the object. Check if the coordinates are close to where the center of the image should be. (Check the image header by clicking Images/Display Header.) Then click OK.

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j) The software then extracts the object. You should see another window appear near the bottom right Data Reduction Results as below. You should record the information for future reference.

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k) Select Tools, then Blink Images. The software creates another window and blinks all three images in succession. Look for any object that “moves” from one image to another. At the top of the tool bar is a series of buttons that controls the blinking-stop blinking(arrow pointing at red circle), the next symbol moves one image back, the next symbol moves the image once forward, and the next continues the blinking automatically through all three images or you can select Tools to choose from the pull down menu. In order to do a thorough check for moving objects especially the discovery of KBOs, you’ll want to focus by looking at a small area and starting from the upper left move to the right then move down so you cover a small area at a time to cover the entire image.

↓

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l) When you notice a “moving” object, stop the blinking and select Tools and choose Show Magnifying Glass or go to the top left of the tool bar. (See arrow) A window appears on the top left of the screen to help you place the cursor on the center of the object. You can change the magnification level by increasing or decreasing it with the buttons next to the magnification button on the tool bar or go to the Tools menu. You may use the cursor keys to move the cursor.

↓

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m) After placing the cursor on the center of the object, select it by left clicking. A window appears on the screen. Check to see if you are satisfied with the placement of the cursor. If you are not satisfied with the placement of the cursor, select reject and try to center the cursor again. Another way to center the cursor is to get it close to the object and while holding the shift key down left click to select the object. If you agree, then click on the button with three dots. (See arrow)

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n) The software will identify the object you selected. Check the columns dRA and dDe. If you are where the software expected that object to be, there should be zeros in the columns. If you get large numbers, then you should try to redo the object again. See below.

o) Select OK and you’ll see that the computer has now put in the Object Designation in the box, then select Accept and the object on the screen will have a designation. See below.

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p) Do this process for each of the three images. Then you can go to Windows and close all images before starting to Load Images for another object.

You may want to explore the option for the Astrometrica software to search for object using Moving Object Detection (under Astrometry) instead of blinking. However, be sure you report only objects that you see on the images and also, the software may not “see” what the human eye can. Another option may arise when using Astrometrica is when the automatic Data Reduction Results do NOT appear as expected due to the three images not aligning and you may have to align the images manually. Keep in mind that you should have at least seven (7) Ref. stars in the Data Reduction Results. WARNING: Again, when opening Astrometrica, if you have any data that was not sent to the MPC, answer NO, to the window asking if you want to replace existing files or it will eliminate all the data. This will allow you to continue to add to your report to be submitted later.)